This invention relates to an apparatus for imparting a specific effect to a television picture image, in which a plurality of television picture image signals are combined to produce one television picture image signal.
There is developed a technique of combining, for example, a black-dotted TV picture image A as shown in FIG. 1 and a hatched TV picture image B as shown in FIG. 2 to produce a combined picture image with the picture image A and B portions demarcated by a diagonal line as shown in FIG. 3. There is also developed a technique for combining a picture image A as shown in FIG. 1 and a picture image B as shown in FIG. 2 to produce a combined picture image signal consisting of a picture image A portion, picture image B portion and overlapped picture image portion C. Although a boundary line of the two picture images in the combined picture image signal is shown as a straight line as shown in FIGS. 3 and 4, it can be displayed in any other pattern. The combined TV picture image signal as shown in FIGS. 3 and 4 are obtained by combining a TV picture image A signal at one channel and TV picture image B signal at the other channel at a channel mixing circuit. In order to obtain a television picture image as shown in FIG. 3 a control signal may be so imparted to the channel mixing circuit, when a TV picture image A signal is switched to a TV picture image B signal during the portion of a horizontal scanning period as to permit a switching time to be sequentially shifted left (in a forward direction) from the end of the horizontal scanning period for each horizontal scanning. If the picture image A signal is momentarily switched to the picture image B signal, a combined picture image signal as shown in FIG. 3 is obtained having a single clear-cut boundary line between the picture image A portion and the picture image B portion. A gradual switching from the picture image A signal to the picture image B signal results in a combined picture image signal having an overlapped portion C, as shown in FIG. 4, between the picture image A portion and the picture image B portion. In this case, it is preferred that the overlapped picture image portion C of the combined picture image signal extend an equal distance toward each of the picture image A and B portions with a marginal corner-to-corner diagonal line as a center. In the conventional apparatus, however, such a marginal corner-to-corner diagonal line is displaced from the center of the two picture images, failing to obtain a desired composite picture image signal. If, for example, the overlapped portion C is displaced toward the picture image B portion, the picture image portion B is intruded by the overlapped picture image portion C and in consequence a correcting operation is necessary.